hree types of results can occur in
DNA testing: inclusion, exclusion,
and inconclusive results. It is important
that victim service providers, investigators,
and prosecutors understand the
meaning of these terms and be able to explain
their implications. While conclusive
results are very reliable, DNA
findings can sometimes yield results that
are difficult to interpret.

Inclusion

When the DNA profile of a known individual
(a victim or suspect) matches
the DNA profile from the crime scene
evidence, the individual is "included"
as a potential source of that evidence.
However, the strength of this inclusion
depends, in part, on the number of DNA
locations examined (up to 13 locations
can be examined) and the statistic reflecting
how often the particular profile
would be found in the general population.
A DNA profile shown to occur rarely in
the population (for example, 1 time in 5
million people) would more strongly suggest
that the individual is the source of
the biological evidence than would a
more common DNA profile (for example,
1 time in 5,000 people). Increasing the
number of DNA locations tested typically
results in more powerful statistics. For this
reason, several DNA locations are tested
whenever possible.

n some cases, a DNA inclusion may provide
information that is of limited value
to the investigative process. For example,
results from samples taken from the victim
may be consistent with the DNA of
the victim, such as vaginal evidence in
sexual assault cases. In addition, if the
suspect wore a condom during the assault,
was aspermatic due to a vasectomy, or did
not ejaculate after the assault, additional
DNA profiles may not be obtained from
the evidence. The results do not mean
the suspect was not present and did not
commit the crime-only that the substance
tested did not come from the suspect.
Additionally, inclusion does not
necessarily mean a suspect is guilty.

Exclusion

When the DNA profile from an individual
(a victim or suspect) does not
match the DNA profile generated from
the crime scene evidence, the referenced
individual is "excluded" as the donor of
the evidence. In some cases, it may be
necessary to perform additional testing to
establish the source of the DNA profile
in the evidence. For example, a blood
sample may be requested from the husband
of a sexual assault victim to determine
whether the DNA profile obtained
from the vaginal swab is the result of a
prior consensual act and not the assault.
Exclusion does not necessarily mean a
suspect is innocent.

Inconclusive
Results

Inconclusive results indicate that
DNA testing did not produce information
that would allow an individual to be either
included or excluded as the source of
the biological evidence. Inconclusive results
can occur for many reasons. For example,
even with sensitive PCR testing,
the quality or quantity of DNA obtained
from the biological evidence may be insufficient
to produce definitive DNA typing
results. Inconclusive results also can
occur if the evidentiary sample contains a
mixture of DNA from several individuals
(for example, a sample taken from a victim
of a gang rape). Even if the suspect's
DNA profile is found in the biological
evidence, the presence of DNA from
other sources may prohibit the establishment
of an inclusive or exclusive result. If
there is more than one perpetrator or if in
a sexual assault case the victim recently
had consensual intercourse in which
semen also may have been deposited in
the victim's vaginal region, the results
could contain profiles from more than
one person. When this happens, it
is often not possible to determine which
specific types came from which donor.
The suspect cannot be excluded as a possible
donor of the DNA found in the evidence
sample, but a more conclusive
result may not be possible. These cases
must be reported as inconclusive. As with all DNA results, inconclusive findings
should be interpreted in the context of
the other evidence in a case.